Auxiliary Examinations for Uremia

1. Blood Routine Examination

In uremia, hemoglobin levels typically fall below 80 g/L, often ranging from 40–60 g/L, presenting as normocytic normochromic anemia. In cases of chronic blood loss or malnutrition, microcytic hypochromic anemia may occur. White blood cell counts generally show little change but may increase during acidosis or infection. Platelet counts are often low or normal, though their function is impaired. The erythrocyte sedimentation rate is frequently elevated due to anemia and hypoproteinemia.

2. Urine Routine Examination

Urinary changes in uremia vary significantly depending on the underlying disease. Common features include:
① Decreased urine osmolality: Morning urine osmolality is typically below 450 mOsm/kg, with a low specific gravity, often under 1.018, and in severe cases, fixed between 1.010–1.012. During concentration-dilution tests, nocturnal urine volume exceeds daytime volume, with specific gravity not exceeding 1.020 and a difference between the highest and lowest specific gravity less than 0.008.
② Reduced urine output: Often below 1000 ml/day, and in advanced stages, when creatinine clearance drops to 1.0–2.0 ml/s, anuria may occur.
③ Proteinuria: Ranges from + to +++, though in late stages, as most glomeruli are destroyed, proteinuria may decrease.
④ Urinary sediment: Contains varying amounts of red blood cells, white blood cells, epithelial cells, and granular casts. The presence of short, homogenous, waxy casts with notched edges is diagnostically significant.

3. Renal Function Tests

During the compensatory phase of renal insufficiency, creatinine clearance may decline, but blood creatinine remains normal. In the azotemia phase, blood creatinine rises, yet clinical symptoms of uremia or metabolic acidosis are absent. In the uremic phase, when creatinine clearance falls below 25 ml/min, blood creatinine significantly increases, accompanied by metabolic acidosis.

4. Blood Biochemistry Tests

Plasma protein levels are reduced, with total protein often below 60 g/L, and albumin typically below 30 g/L. Blood calcium is low, around 2 mmol/L, while blood phosphorus often exceeds 1.7 mmol/L. Blood potassium and sodium levels vary depending on the condition.

5. Other Examinations

(1) X-ray Imaging: Abdominal X-ray plain films are used to assess kidney size, shape, and the presence of urinary tract stones. Lateral abdominal films can reveal atherosclerosis. In severe renal insufficiency, contrast agents are poorly excreted, leading to poor visualization, so contrast-enhanced imaging is generally avoided.
(2) Radionuclide Renography and Renal Scanning: These help evaluate kidney size, blood flow, secretion, and excretory function.
(3) Renal Ultrasound and CT: These are useful for determining kidney position, size, cortical thickness, and the presence of hydronephrosis, stones, or tumors. In uremia, kidneys typically shrink with thinned cortices. However, in cases caused by secondary conditions like diabetes, lupus, or vasculitis, kidney size may remain normal, though cortical echogenicity increases on ultrasound. Renal ultrasound is economical, convenient, non-invasive, and rapid, making it widely used to assess kidney size and cortical echogenicity.